Field of the Invention
The present invention relates to a misfire detecting apparatus for an internal combustion engine, and particularly to the apparatus for determining a misfire based on a rotational speed parameter indicative of a rotational speed of the engine of which the output shaft is connected via a torsion element to an input shaft of a transmission mechanism.
Description of the Related Art
Japanese Patent Laid-open No. 2008-57492 (JP-'492) discloses an apparatus for determining a misfire based on the rotational speed parameter indicative of a rotational speed of the engine of which the output shaft is connected via a damper (torsion element) to a power transmission mechanism. According to this apparatus, a torque component transmitted from the mechanism on the output side of the damper is calculated, a correcting speed component which affects the rotational speed of the engine output shaft is calculated according to the torque component, and a determination rotational speed is calculated by subtracting the correcting speed component from the detected rotational speed. By performing the misfire determination based on the determination rotational speed, the misfire determination can be performed without influence of the damper.
Japanese Patent Laid-open No. 2006-266253 (JP-'253) discloses an apparatus which performs a misfire determination during the warm-up operation of the engine according to a rotation change parameter indicative of changes in the rotational speed of the engine. According to this apparatus, a rotation change is calculated corresponding to the ignition timing of each cylinder, and a rotation change difference N×d360 and a rotation change difference N×d720 are further calculated. The rotation change difference N×d360 is a difference between the present rotation change and the rotation change at 360-degree crank angle before, and the rotation change difference N×d720 is a difference between the present rotation change and the rotation change at 720-degree crank angle before. The misfire determination is performed based on the rotation change difference N×d360 and the rotation change difference N×d720.
The rotational speed of the engine contains an inertia speed changing component which is a speed changing component inevitably generated with the engine rotation. The inertia speed changing component changes corresponding to a position of the piston in each cylinder. According to the apparatus shown in JP-'253, the rotation change is calculated corresponding to the ignition timing, but the inertia speed changing component is not taken into account in this rotation change calculation. Accordingly, if the calculation timing of the rotation change varies due to a change in the ignition timing, influence of the inertia speed changing component changes, which may deteriorate calculation accuracy of the rotation change. Further, the apparatus of JP-'253 determines a misfire during the warming-up operation of the engine. Consequently, the accelerating operating condition or the decelerating operating condition of the engine are not taken into consideration.
According to the apparatus of JP-'492, influence of the damper can be eliminated. However, influence of the inertia speed changing component and the ignition timing is not taken into consideration at all. Further, the calculation method of the rotational speed for the misfire determination shown in JP-'492 uses an integrating (accumulating) calculation. Therefore, a simpler method is desired.